:07:03
creating the mighty Himalayas
and the Tibetan plateau.
:07:14
Dinosaurs have perished.
:07:17
Mammals multiply.
:07:19
The Atlantic windens
as the Pacific dies.
:07:23
The world we know took form.
:07:30
We now know
the crust of the Earth
:07:32
to consist of a number
of rigid plates.
:07:36
Like great rafts of stone
:07:38
bearing the continents
on their backs
:07:40
these plates sail sluggishly-
inches in years-
:07:44
over the hot, deeper mantle
of the Earth.
:07:48
The plates are
in constant relative motion
:07:51
building apart..
:07:55
colliding...
:07:59
Sliding past one another...
:08:02
overriding other plates...
:08:05
plunging to destruction
:08:06
within the interior
from which they formed.
:08:11
The movements of the plates
are sustained
:08:13
by the continuous creation
of new earth's crust
:08:17
The process- one of four
major tectonic processes-
:08:21
is called "seafloor spreading."
:08:24
lt occurs
within the central rifts
:08:26
of the great mid-ocean ridges
:08:28
which wind for 40,000 miles
across the ocean floors.
:08:33
Beneath these rifts,
Earth's crust is thinnest
:08:37
and the pressures of the magma
rising from the fiery interior
:08:40
are relentless.
:08:43
The magma forces its way upward
:08:45
entering the rift
between the plates
:08:47
spreading the seafloor,
breaking to its surface
:08:51
in spectacular
undersea lava forms.